Device and procedure for the detection of a short circuit or overcurrent situation in a power semiconductor switch

ABSTRACT

A device for detecting a change in voltage across a switch includes a resistive-capacitive network and a timer circuit. The resistive-capacitive network includes an impedance, a first resistive element, and a first capacitive element to provide a signal representative of a voltage across the switch. The timer circuit generates a detection signal that is representative of the change in the voltage across the switch after switching on of the switch. The timer circuit raises a level of the detection signal if the voltage across the switch does not fall below a predetermined value after switching on of the switch. The resistive-capacitive network is configured such that parasitic capacitances of the device are compensated or over compensated so as to prevent the timer circuit from raising the level of the detection signal if the voltage across the switch does fall below the predetermined value after switching on of the switch.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European Patent (EP) Application No.13197267.1, filed Dec. 13, 2013. EP Application No. 13197267.1 is herebyincorporated by reference.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a device for thedetection of a change in the voltage across a power semiconductorswitch. Such devices are used, for instance, for the detection of ashort circuit or overcurrent situation in an IGBT (“Insulated GateBipolar Transistor”).

BACKGROUND

High voltages can be applied and high currents can be conducted in somepower semiconductor switches. Short circuits or overcurrents can quicklylead to thermal destruction of the power semiconductor switches. Powersemiconductor switches can include protective circuits for the detectionof short circuits and overcurrent situations. One way of detecting thesesituations is by indirectly monitoring the current through the powersemiconductor switch by determining the voltage across the powersemiconductor switch. The voltage across the power semiconductor switchshould fall swiftly from a relatively high level in the switched-offcondition (the “switched-off-condition” or “OFF-condition” is acondition of the power semiconductor switch in which it is “open” anddoes not conduct current), to a relatively low level in the switched-oncondition (the “switched-on-condition” or “ON-condition” is a conditionof the power semiconductor switch in which it is “closed” and mayconduct current). Accordingly, a control signal of a power semiconductorswitch (for example a gate-driving signal) has an ON-condition, in whichit keeps the power semiconductor switch closed and an OFF-condition, inwhich it keeps the power semiconductor switch open.

The curve on the lower left in FIG. 1B shows an exemplary change in thecollector-emitter voltage of an IGBT (an IGBT is an exemplary powersemiconductor switch) after a transition from a switched-off conditionto a switched-on condition (the change in a corresponding exemplarycontrol signal 130 is shown above left) in normal operation. As shown,the collector-emitter voltage drops sharply to a very low value (closeto 0 volts, for example between 0 and 10 V). An exemplary short circuitbehavior of an IGBT is shown below right in FIG. 1B. In contrast tonormal operation, the collector-emitter voltage does not fall to thevery low value, but high currents can flow in the IGBT (for examplebetween three and ten times the nominal current of the IGBT). In othershort circuit cases, the collector-emitter voltage first drops to itsvalue under normal operation but rises again after some time. This mayresult in a high thermal loading of the power semiconductor switch whichcan be damaged in a relatively short time. Some IGBTs for example, canwithstand a short circuit for some time (e.g., 10 μs) in the switched-oncondition without damage. Protective circuits for the detection of ashort circuit or overcurrent situation should turn off the powersemiconductor switch before the end of this time period. Similarcharacteristics can also be found in other power semiconductor switchesother than in IGBTs. An overcurrent state may as a short circuit statelead to an increased collector-emitter voltage. The collector-emittervoltage in an overcurrent state may be closer to the collector-emittervoltage in the normal state than in the short-circuit state.

An overcurrent or short-circuit state can also occur a period of timeafter the power switch has been turned on. In this error case, thecollector-emitter voltage can drop to a low value associated with normaloperation before an error occurs (e.g., leading to a short-circuit).This can result in a sharp increase in the collector-emitter-voltage(not shown in FIG. 1B), and can also have the negative effects on thepower semiconductor switch described above.

BRIEF DESCRIPTION OF THE FIGURES

Non-limiting and non-exhaustive embodiments of the invention have beendescribed with reference to the following figures, whereby, if nototherwise specified, the same reference symbols relate to the samecomponents in different figures.

FIG. 1A shows an example device for providing electrical energy.

FIG. 1B shows a variety of signals of the device from FIG. 1A in anormal situation and in an example short circuit and/or overcurrentsituation.

FIG. 2 represents an exemplary control circuit.

FIG. 3 shows an exemplary device for the detection of the voltage changeacross a power semiconductor switch.

FIG. 4 shows another exemplary device for the detection of the voltagechange across a power semiconductor switch.

FIG. 5 shows different signals in the device for the detection of thevoltage change across a power semiconductor switch from FIG. 4.

FIG. 6 shows another exemplary device for the detection of to voltagechange across a power semiconductor switch.

FIG. 7 shows another exemplary device for the detection of the voltagechange across a power semiconductor switch.

DETAILED DESCRIPTION

To enable an in-depth understanding of the present invention, severaldetails will be shown in the following description. However, it is clearto the specialist that these specific details are not necessary toimplement the present invention. Elsewhere, for ease of comprehension,known devices and processes have not been described in detail.

In the present description, a reference to “a version”, “anarrangement”, “an example” or “example” means that a particular feature,a structure or a property that is described in connection with thisversion, is included in at least one version of the present invention.Thus, the phrases “in a version”, “in the form”, “an example” or“example” at different places in this description do not necessarilyrefer to the same version or same example. Furthermore, the particularfeatures, structures or properties can be combined in desired andsuitable combinations and/or sub-combinations in one or more models orexamples. Special features, structures or properties can be included inan integrated circuit, in an electronic circuit, in a circuit logic orin other suitable components which provide the described functionality.Over and above this, it should be noted that the drawings serve asguidance for the specialist and that these are not necessarily drawn toscale.

As shown in FIG. 1B and described previously, during normal operation,the collector-emitter voltage 125 (U_(CE)) of a power semiconductorswitch falls swiftly from a relatively high level to a low level afterturning on of the power semiconductor switch. In particular shortcircuit or overcurrent situations, however, thecollector-emitter-voltage 125 (U_(CE)) may not fall to the low level andremains at a higher level. This characteristic can be utilized byprotective circuits for determining the possible existence of a shortcircuit or overcurrent situation in response to the change in thecollector-emitter voltage and, if necessary, turn off of the powersemiconductor switch. That is, the differences described in the changeof the collector-emitter voltage between normal operation and shortcircuit and/or overcurrent situation can be taken advantage of fordetecting a short circuit or overcurrent situation. As alreadydescribed, parasitic capacitances can trigger an erroneous detection ofa short circuit or overcurrent situation in devices designed for thedetection of a change in collector-emitter voltage of a powersemiconductor switch, by influencing detection signals of a protectivecircuit even after the collector-emitter voltage 125 (U_(CE)) drops to alow level under normal conditions.

For example, in some state-of-the-art circuits, multiple resistances arecoupled in series for the purpose of reducing the value of the sensedcollector-emitter voltage 125 (U_(CE)) of the power semiconductorswitch, which can amount to a few kilovolts. To limit the losses in thiscircuit and also for circuit design reasons, it is desirable in somecircuits to limit the current, with the help of these resistances, to 1mA or lower. Therefore, resistances with values in the mega-ohm rangemay be used. Since the values of parasitic capacitances may be in thepico-farad range and these capacitances are discharged over theresistances in the mega-ohm range, the resultant time constant may be afew microseconds for the parasitic capacitances to discharge. These timeconstants may also be in the range of a desirable short-circuitswitch-off time (as mentioned above, the desirable short-circuitswitch-off time may correspond to the period of time which the powersemiconductor switch may withstand short circuit conditions withoutdamage), which may be in the order of 10 μs for some power semiconductorswitches, and may influence short-circuit or overcurrent detection.

In one example of detecting a short circuit or overcurrent situation, asignal representative of the change in the collector-emitter voltage iscompared to a reference voltage (which can be fixed or variable). If thesignal representative of the change in the collector-emitter voltage isgreater than the reference voltage, a fault is detected. The parasiticcapacitances may cause the signal representative of the change in thecollector-emitter voltage to exceed the reference voltage (due to thetime constants) even though there is no short circuit or overcurrentsituation. Hence the discharging of the parasitic capacitances caninterfere with the detection of a short circuit or overcurrentsituation.

For example, a capacitance may be included in the protective circuitthat is designed to be charged if a level of the collector-emittervoltage 125 (U_(CE)) of the power semiconductor switch lies over apredetermined value after the switching-on procedure. This capacitancemay be further charged by the parasitic capacitances, although thecollector-emitter voltage 125 (U_(CE)) of the power semiconductor switchhas already fallen under the predetermined value. This can result in theprotective circuit erroneously determining the existence of a highcollector-emitter voltage 125 (U_(CE)) and detecting a short circuit orovercurrent condition. These effects are particularly serious for highcollector-emitter voltage 125 (U_(CE)) in the region of severalkilovolts (for example between 2.2 and 4.5 kV in the case of some IGBTs)and for elements with relatively slow switching behavior.

In the devices discussed here, a timer circuit is used in combinationwith a resistive-capacitive network, which compensates orover-compensates the parasitic capacitances. As such the influence ofthe parasitic capacitances on the detection of a short circuit orovercurrent situation is reduced or avoided. As a further result ofthis, erroneous detections of short circuits or overcurrent situationsare avoided. It should be appreciated that the term “compensated”includes a certain degree of under-compensation of the parasiticcapacitances, as long as the value of a detection signal remains belowthe predetermined threshold voltage if the signal representative of thevoltage across the power semiconductor switch falls below apredetermined level after turning on the power semiconductor switch(e.g., in a normal operation mode). In one example, it can be possibleto undercompensate the parasitic capacitances as long as a dynamicvoltage level at the third node falls at least to the value of thepredetermined threshold voltage. If the timer circuit includes acapacitance, it is possible to undercompensate the parasiticcapacitances even further. In this example, the allowed amount ofunder-compensation is determined by a charge of the capacitance of thetimer circuit. In other examples the parasitic capacitances may beundercompensated by up to substantially 5% (i.e., a value of thecapacitances of the resistive-capacitive network between the first andsecond nodes is up to substantially 5% higher than required tocompensate for the parasitic capacitances or a value of the firstcapacitive element is up to substantially 5% lower than required tocompensate for the parasitic capacitances).

FIG. 1A shows a device 100 (also called a power converter) for providingelectrical energy to a load 110. The flow of energy can also be directedin the opposite direction. In this example, element 110 is an energysource. Element 110 can also act as energy source and/or as load indifferent operation modes. Subsequently the device 100 is referred to asa device for providing energy (the energy can be provided at differentoutput terminals). The device 100 includes two power semiconductorswitches 104, 106, which are coupled in series between the input 102 andthe input return 112. Further, device 100 is coupled to receive an inputDC voltage 102 (UN). The device is designed to transfer electricalenergy from an input to an output by controlling the powersemiconductors 104, 106. The load 110 is further coupled to the output.Thus, the device for the supply of electrical energy can control thevoltage, current or a combination of the two supplied to the load 110.In the example shown in FIG. 1A, the power semiconductor switches 104,106 are IGBTs.

Hereafter, the devices and processes will be explained using the exampleof IGBTs. However, the devices for the detection of a change in thevoltage across a power semiconductor switch, the control circuits andthe devices for supply of electrical energy are not limited to use withIGBTs. In fact, they can also be used in combination with other powersemiconductor switches. For example, metal-oxide-semiconductor fieldeffect transistors (MOSFETs), bipolar transistors, IEGTs (“injectionenhancement gate transistors”) and GTOs (“gate turn-off thyristors”) canbe used with devices for the detection of a change in the voltage acrossa power semiconductor switch, control circuits and devices for thesupply of electrical energy. Further devices which are based on galliumnitride (GaN) semiconductors or silicon carbide (SiC) semiconductors mayalso be used for the detection of a change in the voltage across a powersemiconductor switch, control circuits and the devices for supply ofelectrical.

A maximum nominal collector-emitter, anode-cathode or drain-sourcevoltage of a power semiconductor switch in a switched-off state can bemore than 500 V, preferably more than 2 kV.

Moreover, the devices for the detection of a change in the voltageacross a power semiconductor switch, control circuits and devices forsupply of electrical energy, are not limited to use with powersemiconductor switches. Thus, other semiconductor switches can also beused along with the devices for the detection of a change in the voltageacross a power semiconductor switch, control circuits and devices forsupply of electrical energy. The effects and advantages discussed hereoccur, at least partly, also in systems with other semiconductorswitches.

Since IGBTs will be discussed hereafter, the terminals of the powersemiconductor switches may be referred to as “collector”, “gate” and“emitter”. As explained earlier, the devices and processes are howevernot limited to IGBTs. To keep it short, the term “emitter” may alsoinclude the terminal of the corresponding power semiconductor switchreferred to as the “source” or “cathode”. Likewise, the term “collector”may also include the terminal of the corresponding power semiconductorswitch referred to as the “drain” or “anode”, and the term “gate” mayalso include the terminal referred to as the “base”. As a result, theterm “collector-emitter voltage” also includes “drain-source voltage”and a “cathode-anode-voltage”, the term “collector voltage” and “emittervoltage” also includes “drain voltage” or “anode voltage” or “sourcevoltage” or “cathode voltage”.

The power semiconductor switches 104,106 are each controlled by thefirst and second control circuits 118, 120 (an exemplary control circuitis shown in connection with FIG. 2). These provide a first and secondgate-emitter driver signal 130,132 (U_(GE1), U_(GE2)) for controllingthe switching of the first and second IGBTs 104, 106. Both controlcircuits 118, 120 can, in turn, optionally be controlled by a systemcontroller 114. The system controller 114 is illustrated as including aninput which may be coupled to receive system-input signals 116. In theexample of FIG. 1A, the two power semiconductor switches 104, 106 areshown in a half bridge configuration. The devices for the detection of achange in the voltage across a power semiconductor switch, controlcircuits and devices for supply of electrical energy can, however, mayalso be utilized in other topologies. For example, a single powersemiconductor switch (e.g. a single IGBT) can be coupled with a devicefor the detection of a change in the voltage across a powersemiconductor switch or a control circuit. In other examples, in a threephase system with six power semiconductor switches or twelve powersemiconductor switches, each of the power semiconductor switches canhave a device for the detection of change in the voltage across a powersemiconductor switch.

In addition to outputting gate-emitter driver signal, the controlcircuits 118, 120 also receive signals which represent voltages of thepower semiconductor switches 104, 106. The signals could be voltagesignals or current signals. In the example shown in FIG. 1A, eachcontrol circuit 118, 120 receives a signal that is representative of thecollector-emitter voltage and is referred to as collector-emittervoltage signal 122, 124 (U_(CE1), U_(CE2)).

In FIG. 1A, the control circuits 104, 106 are drawn as separate controlcircuits. However, both control circuits 104, 106 can also be combinedinto a single control circuit. In the example of a single controlcircuit, the single control circuit controls both of the powersemiconductor switches 104, 106. Further, the second gate-emitter-driversignal 132 (U_(GE2)) may be the inverted first gate-emitter-driversignal 130 (U_(GE1)).

Both control circuits 118, 120 include a device for the detection of achange in the voltage over a power semiconductor switch. With therespective collector-emitter voltage signals 122, 124 (U_(CE1),U_(CE2)), a short circuit and/or overcurrent situation of the respectivepower semiconductor switch can be determined. When a short circuitand/or overcurrent situation is detected, the respective powersemiconductor switch 104, 106 may be switched off.

FIG. 1B shows a variety of example signals for the device shown in FIG.1A for providing electrical energy to a load in a normal condition andin a short circuit and/or overcurrent situation. The topmost curve inFIG. 1B shows an example control signal 130 (U_(GE)) of the powersemiconductor switch. The voltage level of the control signal 130switches between a voltage V_(OFF) in the switched-off condition to avoltage V_(ON) in the switched-on condition. The values of V_(OFF) andV_(ON) can be chosen as desired. In an example, the control signal 130drives the gate of the power semiconductor switch and the values ofV_(OFF) and V_(ON) correspond to the gate-emitter voltage of the powersemiconductor switch in the switched-off or the switched-on state. Forexample, a value for the voltage V_(OFF) for driving the IGBTs in theswitched-off state can vary between −20V and 0V (preferably between −15Vand −10V) and a value for the voltage V_(ON) for driving the IGBTs inthe switched-on state can vary between 10V and 20V (preferably between14.5 V and 15.5 V). For power-MOSFETs, regarding the values of V_(OFF)and V_(ON), the voltage of the gate-source voltage can correspondrespectively to the voltage of the power-MOSFET in the switched-off orthe switched-on condition. For example, a value for the voltage V_(OFF)for power-MOSFET can be between −15V and 0V and a value for the voltageV_(ON) for MOSFETs between 10V and 20V.

FIG. 2 shows an example control circuit 218 (which is one example of thecontrol circuits 118, 120 from FIG. 1A). The control circuit 218includes: A device for the detection of a change in collector-emittervoltage 242 (labeled as UCE detection circuit), a comparator 244, adriver circuit 236 and an optional driver interface 234. The device forthe detection of a change in the voltage across a power semiconductorswitch 242 and the comparator 244 can be combined in a short circuit orovercurrent protection circuit 240. However, both components may also beincluded separately in the control circuit 218. In an example, thecomparator 244 may be included in the driver circuit 236 and the drivercircuit 236 receives the detection signal 246 (U_(DET)) outputted by thedevice for detecting a change in the voltage across a powersemiconductor device 242.

The device for the detection of a change in the voltage across a powersemiconductor switch 242 receives a signal 222, which is representativefor the collector-emitter voltage of a power semiconductor switch (forexample signals 122 or 124 from FIG. 1A). In response to this signal222, which is representative of the collector-emitter voltage of thepower semiconductor switch, the device for the detection of a change inthe voltage across a power semiconductor switch 242 generates thedetection signal 246 (U_(DET)), which is representative of a change inthe voltage across a power semiconductor switch after switching on thepower semiconductor switch.

The short-circuit or overcurrent protection circuit 240 is coupled toreceive a reference signal 248 (U_(REF)). The comparator 244 comparesthe reference signal 248 (U_(REF)) and the detection signal 246(U_(DET)) and determines whether a short circuit and/or overcurrentcondition exists. In one example, the short-circuit and/or overcurrentprotection circuit 240 detects that the short-circuit and/or overcurrentcondition exists when the detection signal 246, which is representativeof the collector-emitter voltage of a power semiconductor switch afterswitching on the semiconductor power switch, is greater than thereference signal 248. The reference signal 248 may be an externalreference signal, or may be supplied from the driver circuit 236 to theshort-circuit and/or overcurrent state protection circuit 240.

As already described above, the collector-emitter voltage of the powersemiconductor switch should quickly drop to a relatively low value afterthe power switch is turned on. A collector-emitter voltage whichincreases above a predetermined value may be indicative of the presenceof a short-circuit and/or overcurrent state. The lower curves in FIG. 1Billustrate this. A normal switching on process is shown on the left sideof FIG. 1B. The collector-emitter voltage 125 (U_(CE)) decreases rapidlyafter the switching on event. The device generates a detection signal(U_(DET)) from a signal which is representative of the collector-emittervoltage of 125 (U_(CE)) in order to detect the changes in the waveformof a collector-emitter voltage 242. The detection signal 246 (U_(DET))should remain below the reference signal 248 in the circuit of FIG. 2when the example waveform of the collector-emitter voltage 125 (U_(CE))is as shown on the left in FIG. 1B. In this case, correctly, no shortcircuit or overcurrent is detected. As already mentioned above, thedevice for the detection of a voltage over a power semiconductor switchmay prevent a false detection of a short circuit and/or overcurrentstate, which may occur due to parasitic capacitances present in thedevice. This prevention of false detection of a short circuit and/orovercurrent state can be provided for different voltage levels of thecollector-emitter voltage (e.g., from 200 V to 4.5 kV) or for differentswitching delays of different power semiconductor switches.

The short-circuit and/or overcurrent protection circuit 240 can outputan error signal U_(FT) 250 if a short-circuit and/or overcurrent stateis detected. In the example of FIG. 2, an error signal 250 (U_(FT)) isoutput to the driver circuit 236. In response to the error signal 250,the driver circuit 236 may switch off the power semiconductor switch toprevent damage thereto. However, the error signal can also be processedin other ways in alternative arrangements. For instance, the errorsignal 250 (U_(FT)) may be provided to a further control element. Thisfurther control element can switch off two or more power semiconductorswitches in a predetermined order.

As already described above, the driver circuit 236 can receive an errorsignal 250 that indicates a short-circuit and/or overcurrent state, andturn off the power semiconductor switch in response to a detectedshort-circuit and/or overcurrent state. One or more components of theshort-circuit and/or overcurrent state protection circuit 240 may beoptionally included in the driver circuit 236. For example, thecomparator 244 may be included in the driver circuit 236 and the drivercircuit may receive the reference signal 248 (U_(REF)) and the detectionsignal 246 (U_(DET)) which is representative of the change of thecollector-emitter voltage. In another example, the reference signal 248may be generated internally to the driver circuit and the driver circuitincludes the comparator 244. As such the driver circuit receives thedetection signal 246. In addition, the driver circuit 236 may alsosupply a gate-emitter-driver signal 230 (U_(GE)) to control the powersemiconductor switch.

In the example of FIG. 2, the driver circuit 236 is coupled with theoptional driver interface 234 via a galvanic isolation 238 (for examplea transformer) in order to receive control signals from the systemcontroller 214. The driver interface 234 may in turn be coupled to thesystem controller 214, which receives the system inputs 216. The drivercircuit 236 may be controlled by the received system inputs 216.

FIG. 3 shows an example device for the detection of a change in avoltage across a power semiconductor switch 342 (which is one example ofthe detection circuit 242 in FIG. 2) which may be utilized in a controlcircuit for a power semiconductor switch. The device for the detectionof a change of a voltage across a power semiconductor switch 342includes: a resistive-capacitive network 352, a timer circuit 362 andoptional first and second clamping circuits 358, 360.

An input signal 322 (U_(CE)), which is representative of acollector-emitter voltage of a power semiconductor switch, may becoupled at a first node of the resistive-capacitive network 352. Theresistive-capacitive network 352 also provides an output signal, whichis also representative of the collector-emitter voltage of a powersemiconductor switch (at a lower voltage level than the input signal 322(U_(CE))) at a second node A. The timer circuit 362 is coupled 361 tothe second node A through a resistive element 372 (and optionally viafurther elements). The timer circuit 362 is thus also coupled to a thirdnode of the resistive-capacitive network 352. The timer circuit 362generates a detection signal 346 (U_(DET)) in response to a voltage atthe third node of the resistive-capacitive network 352, the detectionsignal 346 (U_(DET)) is representative of a change of thecollector-emitter voltage of a power semiconductor switch after turningon the power semiconductor switch. In some examples, the timer circuit362 includes a capacitance, which is designed to be charged to apredetermined threshold voltage in the event of the voltage at secondnode A 368 not falling beneath a predetermined value after turning onthe power semiconductor switch. The voltage applied across the capacitorof the timer circuit 362 can thus be used as a detection signal 346(U_(DET)). The timer circuit can also be implemented with othercircuits. For instance, a digital circuit can be utilized as timercircuit.

The resistive-capacitive network 352 includes a first capacitive element370 coupled between the second node A and a fourth node of theresistive-capacitive network 352. The fourth node of theresistive-capacitive network 352 is at a second reference potential 366(V_(L)). In addition, the resistive-capacitive network 352 includes, asdescribed above, the first resistive element 372 coupled between thesecond node A and the third node. One or more impedances 355, 356 arecoupled between the first node receiving the input signal 322 (U_(CE))and the second node A 368.

A first optional clamping circuit 358 is coupled between the third nodeof the resistive-capacitive network 352 and a first reference potential364 (V_(H)). The first optional camping circuit 358 is designed to limitthe voltage at the third node to the first reference potential 364(V_(H)). The value of the first reference potential 364 (V_(H)) can beselected to be less than a level of the input signal 322 (U_(CE)). Thefirst reference potential 364 (V_(H)) can also vary with time. As thislevel can correspond to a (possibly high) collector-emitter voltage ofthe power semiconductor switch, the value of the first referencepotential 364 (V_(H)) can be set below a tenth or even below a hundredthof the peak level of the input signal 322 (U_(CE)).

In addition, the value of the first reference potential 364 (V_(H)) canbe selected to be more than the level of the reference signal U_(REF)248 (see FIG. 2), when a comparator as shown in FIG. 2 is used in orderto compare the detection signal 346 with a reference signal for thedetection of a short-circuit or overcurrent state. In one example, thevalue of the control signal 130 (U_(GE)) in the switched on state (i.e.the value V_(ON)) may be utilized as the second reference potential 364(V_(H)). This may be advantageous as this voltage may already beavailable in the driver circuit 236 (see FIG. 2).

As long as the input signal 322 (U_(CE)) has a high enough value suchthat the voltage level at the third node of the resistive-capacitivenetwork is greater than the first reference potential 364 (V_(H)) (andoptionally the additional a voltage drop across elements of the firstclamping circuit 358, e.g. a diode), the voltage at the third node issubstantially clamped to the first reference potential (V_(H)) by thefirst clamping circuit 358 (and a potential voltage drop over elementsof the first clamping circuit, e.g. a diode). In this state, theelements of the resistive-capacitive network 352 form aresistive-capacitive voltage divider in the dynamic equivalent circuit.In the dynamic equivalent circuit, the first resistive element 372 iscoupled in parallel with the first capacitive element 370 (since thereis only a stationary voltage difference between the second referencepotential 366 (V_(L)) and the first reference potential 364 (V_(H)), thethird node and fourth node are shorted in the dynamic equivalentcircuit). The first resistive element 372 and the first capacitiveelement 370 can thus be combined as a (virtual) first impedance 354. Thedynamic portion of the input signal 322 (U_(CE)) drops over the one ormore impedances 355, 356 and the first impedance 354. As a result, atthe second node A 368, the dynamic component of the input signal 322(U_(CE)) is divided according to the ratio of the one or more impedances355, 356, and the first impedance 354.

When the input signal 322 (U_(CE)) has dropped to a low enough valuesuch that the voltage level at the third node of theresistive-capacitive network is less than the first reference potential364 (V_(H)) (and a potential a voltage drop across elements of the firstclamping circuit 358, such as a diode), the first clamp circuit 358 doesnot clamp the voltage at the third node of the resistive-capacitivenetwork. In this case, the elements of the resistive-capacitive network352 again form a resistive-capacitive voltage divider in the dynamicequivalent circuit, where optional resistive elements of the timercircuit 352 are dynamically connected in series with the first resistiveelement 372. The additional resistive elements of the timer circuit 352can lead to a change in the dynamic properties of theresistive-capacitive voltage divider. Nevertheless, the dynamiccomponent of the input signal 322 (U_(CE)) is again divided down at thesecond node A 368.

In both modes described above, the resistive-capacitive voltage dividerformed by the resistive-capacitive network 352 (and optional elements ofthe timer circuit 362) divides a dynamic component of the input signal322 (U_(CE)) to a lower voltage level at the second node A.

A number of the impedances of resistive-capacitive network 352 can befreely selected. Thus, a desired value of the voltage level at node Afor a predetermined voltage level of the input signal 322 (U_(CE)) canbe adjusted by various different combinations of impedances. It ispossible on the one hand, to couple a larger number of impedances oflower value in series. On the other hand, a small number, or even onlytwo impedances can be used with the higher valued impedances. In oneexample, the impedances can be selected so that a current flowing in theresistive-capacitive network 352 when connected to a collector-emittervoltage (U_(CE)) of a power semiconductor switch does not exceed apredetermined current level (e.g., a mean current of 1.5 mA).

As described above, the resistive-capacitive network 352 compensates forthe parasitic capacitances of the device for the detection of the changein the voltage across a power semiconductor switch 342, orovercompensates the parasitic capacitances. The voltage at the secondnode A therefore decreases as input signal 322 (U_(CE)) decreases to alower value as would be the case if the parasitic capacitances of thedevice for the detection of the change in the collector-emitter voltageor drain-source voltage of a power semiconductor switch 342 were notcompensated. The voltage at second node A, however, is lower than thevoltage would be if there was no compensation of the parasiticcapacitances at a predetermined time after the turn-on process hasstarted. As such, the capacitance of the timer circuit 362 is preventedfrom being charged to a value greater than the predetermined threshold(which is also referred to as a reference signal which is used to detectwhether a short circuit or overcurrent event occurs), if noshort-circuit or overload condition exists (an example waveform of theinput signal 322 (U_(CE)) is shown on the left hand side of FIG. 1B). Ifalternative timer circuits are utilized, a lower voltage level at thesecond node A may also further prevent the detection signal with anoverly high level from being outputted and, as a result, a falsedetection of a short-circuit or overcurrent condition may occur.Furthermore, changes in the input signal 322 (U_(CE)) may be propagatedwithout substantial delay to the second node A with the use of theresistive-capacitive network 352 (which forms an resistive-capacitivevoltage divider in the dynamic equivalent circuit) that.

The second optional clamping circuit 360 is coupled to limit a voltageat the third node to a predetermined minimum voltage. The value of thepredetermined minimum voltage can be selected (an can vary with time) tobe less than the level of the reference signal U_(REF) 248 (see FIG. 2),when a comparator is used as shown in FIG. 2, in order to compare thedetection signal 346 with a reference signal for the detection of ashort-circuit or overcurrent state. In one example, the value of thecontrol signal 130 in the switched off state (V_(OFF)) may be used asthe predetermined minimum voltage. This may be advantageous as thisvoltage may already be available in the driver circuit 236 (see FIG. 2).In addition, the second clamping circuit 360 can clamp the level of thethird node to the second reference potential (V_(L)) 366 of the fourthnode of the resistive-capacitive network 352. The second optionalclamping circuit can be utilized to protect the device for detecting achange of the voltage across a power semiconductor switch 352 and thecomponents coupled to this device (e.g., a drive circuit 236 of FIG. 2).

FIG. 4 illustrates a further exemplary device for the detection of achange of a voltage over a power semiconductor switch 442. Like thedevice in FIG. 3, the device in FIG. 4 includes: a resistive-capacitivenetwork 452, a timer circuit 462 and optional first and second clampingcircuits 458, 460. It should be appreciated that these coupled andfunction as described in reference to FIG. 3.

A first capacitive element 470 of the resistive-capacitive network 452is coupled between a second node A 468 and a fourth node. For example,the voltage at the fourth node can be substantially the predeterminedminimum voltage of a second clamping circuit 460. Additionally, a firstresistive element 472 (R₁) is coupled between the second node A 468 andthe third node of the resistive-capacitive network 452. The firstresistive element 472 (R₁) can have a value between 10 kΩ and 1 MΩ. Asdiscussed in connection with FIG. 3, the first resistive element 472(R₁) and the first capacitive element 470 form, in the dynamicequivalent circuit, a first (virtual) impedance 454 of aresistive-capacitive voltage divider.

Further, the resistive-capacitive network 452 has one or severaladditional impedances 455, 456 that are coupled between the second nodeA 468 and the first node of the resistive-capacitive network 452, andcoupled to the collector-emitter voltage 422 (U_(CE)). In the example ofFIG. 4, the resistive-capacitive network 452 includes N−1 additionalimpedances 455, 456 (where N is an integer larger than one). Inaddition, each of the N−1 impedances 455, 456 has a further capacitiveelement 474, 478 (C₂, C_(N)) and a further resistive element 476, 480(R₂, R_(N)) coupled in parallel with its respective capacitive element474, 478 (C₂, C_(N)). However, this arrangement is not mandatory. Forexample, a plurality of impedances 455, 456 may have a common capacitiveelement, which is coupled in parallel to the respective resistiveelements. Conversely, a plurality of impedances 455, 456 may have acommon resistive element, which is coupled in parallel with therespective capacitive elements.

In one example, the values of the capacitive elements 474, 478 (C₂,C_(N)) of the impedances 455, 456, which are coupled between the secondnode A 468 and the first node of the resistive-capacitive network, aresubstantially the same (for example, between 0.5 pF and 200 pF). Inaddition, the values of the resistive elements 476, 480 (R₂, R_(N)) ofthe impedances 455, 456, which are coupled between the second node A 468and the first node of the resistive-capacitive network, havesubstantially the same value (for example between 10 kΩ and 1 MΩ). Asalso discussed in connection with FIG. 3, the impedances 455, 456 andthe first impedance 454 form, in the dynamic equivalent circuit, aresistive-capacitive voltage divider for dividing a dynamic portion ofthe input signal 322 (U_(CE)).

Additionally or alternatively, the value of the first capacitive element470 (C₁) of the first impedance 454 may be selected to compensate orover-compensate (or slightly under-compensate) for the parasiticcapacitances of the device for the detection of a change of a voltageacross a power semiconductor switch 442. In general, increasing thevalue of one of the additional capacitive elements 474, 478 (C₂, C_(N))shifts the behavior in the direction of over-compensation. Likewise,decreasing the value of the first capacitive element 470 (C₁) shifts thebehavior in the direction of over-compensation. On the other hand,decreasing the value of one of the additional capacitive elements 474,478 (C₂, C_(N)) shifts the behavior in the direction ofunder-compensation. Likewise, increasing the value of the firstcapacitive element 470 (C₁) shifts the behavior in the direction ofunder-compensation. Thus, the value of one or more of the additionalcapacitive elements 474, 478 (C₂, C_(N)) can be higher than in acompensated case to achieve over-compensation. Alternatively, the valueof one or more of the additional capacitive elements 474, 478 (C₂,C_(N)) can be lower than in an exactly compensated case to achieveunder-compensation.

For instance, the value of the first capacitive element 470 (C₁) can bein the range of a few Pico farads to a few tens of Pico farads (forexample, 3 pF to 20 pF) below the value of the additional capacitiveelements 474, 478 (C₂, C_(N)) of the additional impedances 455, 456 tocompensate for the parasitic capacitances. Alternatively, the value ofthe first capacitive element 470 (C₁) can be lower than in thecompensated case to over-compensate the parasitic capacitances (or itcan be higher to under-compensate the parasitic capacitances up to acertain degree). In one example, the value of the additional capacitiveelements 474, 478 (C₂, C_(N)) can be up to 20 pF higher than a value forthe exactly compensated case to overcompensate the parasiticcapacitances.

In addition, each capacitive element of the resistive-capacitive voltagedivider 452 has a value corresponding to at least eight times the valueof the parasitic capacitances of the device for detecting a change of avoltage across a power semiconductor switch 442.

In the device for the detection of a change of a voltage across asemiconductor power switch 442 shown in FIG. 4, first and secondclamping circuits 458, 460 can be provided which function similar to thecorresponding first and second clamping circuits 358, 360 in FIG. 3. Inone example, the first and second clamping circuits 458, 460 may eachinclude a diode.

An optional resistive element 471 (R_(E)) may be coupled in parallel tothe first capacitive element 470. The optional resistive element 471(R_(E)) can be designed to determine a stationary/constant value of thedetection signal 446 (at least partially). It can have a value between 1MΩ and 20 MΩ. If the voltage level of the collector-emitter voltage(U_(CE)) is approximately stationary/constant sometime after a switchingevent, then the voltage at second node A 468 is at least partiallydetermined through the resistive elements of the resistive-capacitivevoltage divider 452. Then, the optional resistive element 471 (R_(E))can be utilized to determine, at least partially, the voltage level atsecond node A. The voltage level at node A influences to what voltagelevel of a capacitance of the timer circuit 462 (see below) is chargedor discharged to in both a normal situation and in a short circuit orovercurrent situation and thus the stationary voltage level of thedetection signal 446. The optional resistive element 471 (R_(E)) thuscan be selected to partially adjust the stationary/constant value of thedetection signal 446. Without the optional resistive element 471 (R_(E))the stationary level of the voltage at the second node A is the level ofthe input signal 422 (U_(CE)) if the first or second clamping circuits458, 460 do not conduct.

As has already been described, the resistive-capacitive network 452compensates for the parasitic capacitances of the device for thedetection of a change of a voltage across a power semiconductor switch442 (or over-compensates the parasitic capacitances). Various componentscan contribute to the parasitic capacitances depending on the specificdesign of the device 442. For example, PCB layout capacitances maycontribute to the parasitic capacitance of the device for the detectionof a change of a voltage across a power semiconductor switch 442. Inaddition, capacitances of the diodes of the first and second clampingcircuits 458, 460 can also contribute to the parasitic capacitances ofthe device for the detection of a change of a voltage across a powersemiconductor switch 442. In one example, the PCB layout capacitanceslie in parallel to the first capacitive element 470 (C₁) as parasiticcapacitances.

The timer circuit 462 includes an RC element including the capacitance484 (C_(T)) and a resistive element 482 (R_(T)). The voltage at one endof the capacitance 484 (C_(T)) of the timer circuit 462 may be thedetection signal 446 which is representative of a change of thecollector-emitter voltage of a power semiconductor switch after aswitching on event of the power semiconductor switch. The timer circuitcan also be designed in a different manner. For example, a digitalcircuit can sample a voltage level at the third node of theresistive-capacitive network 452 and generate the detection signal 446in response to the voltage level at the third node.

If a comparator is used to compare the detection signal 446 with areference voltage to detect a short-circuit or overcurrent state as inFIG. 2, the capacitance 484 (C_(T)) is maintained at a level below thereference voltage as long as the power semiconductor switch is in an offstate. For example, the capacitance 484 (C_(T)) can be held to a voltagelevel of the control signal 130 in the off state, V_(OFF).

In one example, the first end of the capacitor 484 (C_(T)) can beconnected to a switch (not shown in FIG. 4). If the power semiconductorswitch is switched off, the switch can clamp the first end 484 of thecapacitance (C_(T)) to a level below the reference voltage. Thecapacitance 484 (C_(T)) is then discharged until the level below thereference voltage is reached (not shown in FIG. 5).

After the power semiconductor switch turns on, the capacitance 484(C_(T)) of the timer circuit 462 is charged so that the voltage level ofthe detection signal 446, which is representative of a change of thecollector-emitter voltage of a power semiconductor switch afterswitching on the power semiconductor switch, increases. If, as discussedin the last paragraph, a switch is used to clamp the first end of thecapacitance 484 (C_(T)) to a level below the reference voltage, theswitch is opened in response to the turning on the power semiconductorswitch. The first end of the capacitance 484 (C_(T)) is hereby releasedand the voltage level of the detection signal 446 can rise in responseto a change of the collector-emitter voltage of the power semiconductorswitch.

However, if the collector-emitter voltage 422 (U_(CE)) does not fallbelow a predetermined value after the switching on event of the powersemiconductor switch, then the capacitance 484 (C_(T)) of the timercircuit 462 is charged above the predetermined threshold voltage (forexample, the voltage level of the reference signal 248 in FIG. 2). Thisbehavior is shown on the right hand side of FIG. 5. The characteristicsof the drive signal 530, the collector-emitter voltage 522, voltage atnode A 568, and the detection signal 546 are shown under short circuitconditions on the left hand side of FIG. 5. The upper waveform shows anexemplary control signal 530 (U_(GE)). As shown on the right hand sideof the middle waveform, the collector-emitter voltage 522 (U_(CE)) ofthe power semiconductor switch only falls slightly in the case of ashort circuit, and then returns to a relatively high level. In othershort-current situations the collector-emitter voltage may initiallydrop to its normal mode level and returns to a higher level after sometime. As a result, a voltage level at node 568 A (V_(A)) is higher thanunder normal conditions. As a result, the voltage of one end of thecapacitance of the timer circuit (i.e. the detection signal 546)increase above the voltage level of the reference signal 568 (U_(REF)).In other words, the capacitance 484 is charged such that the detectionsignal 546 increases above the predetermined threshold voltage. Ashort-circuit or an overcurrent protection circuit (for example, circuit240 in FIG. 2) can detect this rise and can determine there is an errorand can output a corresponding error signal. As a result, a controlcircuit can turn off the power semiconductor switch, and an ON time 531(t_(ON)) is shortened and the power semiconductor switch may not bedamaged. The time constant of the rise of the detection signal 546 maybe at least partially determined by the values of the capacitance 484(C_(T)) and the resistive element 482 (R_(T)) of the timer circuit 462.The capacitance 484 (C_(T)) can also be charged above the voltage levelof the reference signal 548 (U_(REF)) if a short-circuit or overcurrentsituation occurs after the collector-emitter voltage of the powersemiconductor switch has dropped to its stationary/constant level in anon state.

However, if the collector-emitter voltage 422 (U_(CE)) falls below thepredetermined value after turning on the power semiconductor switch, thedevice 442 prevents the voltage of the capacitance 484 (C_(T)) of thetimer circuit 462 from increasing above the predetermined thresholdvoltage (for example, the voltage level of the reference signal 248 inFIG. 2). In other words, the device 442 prevents the capacitance 484from being charged such that the detection signal 546 does not increaseabove the predetermined threshold voltage. This behavior is againillustrated by FIG. 5. The waveform characteristics of the drive signal530, the collector voltage 522, voltage at node A 568, and the detectionsignal 546 are shown under normal conditions on the left hand side ofFIG. 5. An exemplary control signal 530 (U_(DR)) of a powersemiconductor switch is again outlined right at the top. The length ofON time 531 (t_(ON)) and the length of OFF time 533 (t_(OFF)) can becontrolled by a system control (for example, system control 214 in FIG.2) in accordance with the requirements of the power converter. Thecontrol circuit 218 can additionally turn off the power semiconductorswitch in response to different errors (e.g., in response to errorsignal 250 (U_(FT)) in FIG. 2). As shown in the middle curve on theleft, the collector-emitter voltage 522 (U_(CE)) of the powersemiconductor switch falls significantly in the normal condition (to alevel close to 0 V). At the same time, the voltage level falls at thesecond node A 568 (U_(A)). As a result, the capacitance of the timercircuit is initially charged, so that the voltage level of the detectionsignal 546 increases. However, if the collector-emitter voltage 522(U_(CE)) of the power semiconductor switch (and hence the voltage atnode A 568) falls below a predetermined value, the capacitance of thetimer circuit is not further charged. On the contrary, the device 442for the detection of a change of a voltage over the power semiconductorswitch may discharge the capacitance 484 of the timer circuit 462. Thusthe voltage level of the detection signal 546 remains below a referencevoltage 546 and the short-circuit or overcurrent detection circuit isnot triggered.

By employing the first clamping circuit 458, a timing detection of ashort-circuit or overcurrent state can be largely independent of theamplitude of the collector-emitter voltage (U_(CE)) of the powersemiconductor switch in the switched off state. For example, thedetection timing can be about 4 to 20 microseconds after a switchingevent, regardless of the value of the collector-emitter voltage (U_(CE))of the power semiconductor switch (e.g., 1.2 kV in a first mode ofoperation and 4.5 kV in a second mode of operation). As described above,the first clamping circuit 458 can clamp the voltage level at the thirdnode of the resistive capacitive network 462 to a first referencepotential 464 (V_(H)), as long as the voltage level at the second node Ais above the first reference potential 464 (V_(H)) and optional voltagedrops over components of the first clamping circuit 458. If a resistiveelement 471 (R_(E)) is coupled in parallel to the first capacitiveelement 470, as in the device for detecting a change in the voltageacross a power semiconductor switch 442, the first clamping circuit 458clamps the voltage at the third node as long as the divided input signal422 (U_(CE)) has a higher level than the first reference potential 464(V_(H)) and optional voltage drops of the first clamping circuit'scomponents. This is independent of the respective collector emittervoltage (U_(CE)) of the power semiconductor switch in the off state. Inaddition, the capacitance is 484 (C_(T)) of the timer circuit 462 can becharged at the same rate independently of the respective value of thecollector-emitter voltage (U_(CE)) of the power semiconductor switch.

In the previous examples it has been discussed how aresistive-capacitive network can compensate the parasitic capacitancesof the device for the detection of the change in the collector-emittervoltage or drain-source voltage of a power semiconductor switch in orderto avoid erroneous detections of a short-circuit or overcurrent state.However, the capacitive elements of the resistive-capacitive networkneed not necessarily be additional components. In one example, one ormore of the capacitive elements of the resistive-capacitive network canbe formed by the parasitic capacitances of the device for the detectionof the change in the collector-emitter voltage or drain-source voltageof a power semiconductor switch themselves. For instance, PCB layoutcapabilities of the device for the detection of the change in thecollector-emitter voltage or drain-source voltage of a powersemiconductor switch may be used as elements of a resistive-capacitivenetwork. The arrangement of the components of the device for thedetection of the change in the collector-emitter voltage or drain-sourcevoltage of a power semiconductor switch may be chosen such that PCBlayout capabilities have suitable values to act so as one or more of thecapacitive elements of the resistive-capacitive network.

The device for the detection of a change of a voltage across asemiconductor power switch 642 according to FIG. 6 includes thecomponents of the device for the detection of a change of a voltageacross a power semiconductor switch 442 according to FIG. 4. Inaddition, the device 642 according to FIG. 6 has a further capacitiveelement 686 (C_(C)), which is coupled between node A 668 and a first endof the first capacitive element 670. The value of the additionalcapacitive element 686 (C_(C)) may be significantly smaller (one fifthor less, or one-tenth or less) than the value of the capacitive element670 (C₁). In this case, the capacitance between the second node A 668and the fourth node (which is at the first reference voltage 666(V_(L))) is nearly equal to the value of the additional capacitiveelement 686 (C_(C)) (approximately equal to

$\left. \frac{1}{{1/C_{c}} + {1/C_{1}}} \right).$

In addition, the additional capacitive element 686 (C_(C)) may besignificantly smaller (one fifth or less, or one-tenth or less) than thecapacitance 684 (C_(T)) of the timer circuit 662. In this way, theinfluence of the capacitive element 670 (C₁) on a voltage level at thesecond node A can be reduced by the additional capacitive element 686(C_(C)), if the signal which is representative for a voltage over apower semiconductor switch is below the reference voltage level. Thiscan affect the charging time of the capacitance 684 (C_(T)) of the timercircuit 662 and thus the period of time until a short circuit orovercurrent state is detected is less strongly influenced by thecollector-emitter voltage (U_(CE)) of the power semiconductor switch inan OFF-state. The additional capacitive element 686 (C_(C)) may alsoreduce variation in the period of time until a short circuit orovercurrent state is detected, especially in the range of relatively lowcollector voltages (U_(CE)) of a power semiconductor switch in the OFFstate (for example, 200 to 400 V).

Additionally or alternatively, more capacitive elements may also beincluded in the other impedances 656, 655 of the resistive-capacitivenetwork 652. Thus, a second additional capacitive element (not shown inFIG. 6) can be inserted in a second impedance and coupled in parallel tothe second resistive element 676 (R₂) and in series to a secondcapacitive element 674 (C₂) of the second impedance. In addition, theend of the second additional capacitive element which is coupled to thesecond capacitive element 674 (C₂) is also coupled to the capacitance ofthe impedance adjacent to the impedance 656. In the example of FIG. 6,if there are no intervening impedances between the impedance 655 and656, the second additional capacitive element may at one end be coupledto resistive elements 676 and 680 (R₂ and R_(N)) and at the other end becoupled to capacitances 674 and 678 (C₂ and C_(N)). This secondadditional capacitive element may be dimensioned to be significantlysmaller (one fifth or less, or one-tenth or less) than the capacitiveelement 674 (C₂) of the second impedance (656). Thus, it functions inrelation to the second capacitive element 674 (C₂) of the secondimpedance 656 in a manner similar to the first additional capacitiveelement 686 (C_(C)) in relation to the capacitive element 670 (C₁) ofthe first impedance (670). The second additional capacitive elementessentially determines the capacitance of the device and reduces theinfluence of the second capacitive element 674 (C₂) on the charging timeof the capacitance 684 (C_(T)) of the timer circuit 662.

Additionally and independently of the additional capacitive elements,the device for the detection of a change of a collector-emitter voltageof a semiconductor power switch 642 according to FIG. 6 has a furtherresistive element 688 (R_(E1)), which coupled in parallel with thesecond capacitive element 674 (C₂) of the second impedance 674. This canhelp to determine a stationary/constant voltage level of the detectionsignal 646 (together with the optional first resistive element 671(R_(E)) which is coupled in parallel with the first capacitive element670 (C₁)). The additional optional resistive elements 688 (R_(E1)) and671 (R_(E)) can also contribute to determining the stationary/constantvoltage level at the node between the further capacitive elements 686(C_(C)), and the optional resistive elements 688 (R_(E1)) and 671(R_(E)). This can prevent stationary overvoltage across the capacitiveelements 670, 674 (C₁, C₂) and the further capacitive element 686(C_(C)). For instance, an isolation resistance of the capacitiveelements 670, 674 (C₁, C₂) and the further capacitive element 686(C_(C)) can be different even for two components having the samespecification. As a consequence, a voltage drop over these components ina stationary state can also vary from circuit to circuit. This, in turn,can result in a voltage over the capacitive elements 670, 674 (C1, C2)or the further capacitive element 686 (CC) exceeding an admissiblevoltage level. In addition, the isolation resistance of the capacitiveelements 670, 674 (C1, C2) and the further capacitive element 686 (CC)can change over time, which also can lead to excess voltages over thesecomponents. Alternative to the optional resistive elements 688 (R_(E1))and 671 (R_(E)) the device for the detection of a change in the voltageacross a power semiconductor switch 642 may include a resistive elementbeing coupled in parallel to the further capacitive element 686 (C_(C)).This resistive element can be at least five to ten times as large as thefirst resistive element 62 (R₁).

The device for the detection of a change of a voltage across a powersemiconductor switch 742 according to FIG. 7 includes the components ofthe device for the detection of a change of a voltage across a powersemiconductor switch 442 according to FIG. 4 apart from the optionalresistive element (R_(E)). In addition, the circuit according to FIG. 7includes an additional resistive element 790 (R_(th)), which is coupledbetween the input of the timer circuit and a lower reference voltage 766(V_(L)). Similar to the optional first resistive member (R_(E)) in thedevices of FIG. 4 or FIG. 6, the additional resistive element 790(R_(th)) may also determine the stationary/constant value of thedetection signal 446 (at least partially). If the voltage level of thecollector-emitter voltage (U_(CE)) is approximately stationary/constantsometime after a switching event, then the voltage at node A 768 is atleast partially determined through the resistive elements of theresistive-capacitive voltage divider 752. Then, the optional additionalresistive element 790 (R_(th)) can be utilized to determine, at leastpartially, the voltage level at node A. The voltage level at node Ainfluences to what voltage level a capacitance of the timer circuit 762(see above) is charged or discharged to in a normal situation and in ashort circuit or overcurrent situation and thus the stationary voltagelevel of the detection signal 746. The optional additional resistiveelement 790 (R_(th)) thus can be selected to partially adjust thestationary/constant value of the detection signal 746.

The timer circuit of FIG. 7 further includes second reference resistor792 (R_(DYN)), a second capacitance 794 (C_(DYN)), and a diode D3 796which are designed to influence a dynamic level of the detection signal746. This can be used to switch on high-voltage IGBTs without massivelyincreasing a detection threshold of a short-circuit or overvoltagedetection circuit. Some high-voltage IGBTs require several tens of μs toreach a steady-state voltage in an ON-state.

The above description of the illustrated examples of the presentinvention is not meant to be exhaustive or limited to the examples.While specific embodiments and examples of the invention are describedherein for illustrative purposes, various modifications are possiblewithout departing from the present invention. The specific examples ofvoltage, current, frequency, power, range values, times, etc., are onlyillustrative, so that the present invention can also be implemented withother values for these magnitudes.

These modifications can be carried out on examples of the invention inthe light of the above detailed description. The terms used in thefollowing claims should not be so construed that the invention islimited to the specific embodiments disclosed in the specification andthe claims. The present specification and figures are illustrative andshould not be regarded as limiting.

What is claimed is:
 1. A device for the detection of a change in the voltage across a power semiconductor switch, the device comprising: a resistive-capacitive network having a first, a second, a third and a fourth node, wherein the resistive-capacitive network is to be coupled to a first terminal of the power semiconductor switch at the first node and to provide at the second node a signal that is representative of a voltage across the power semiconductor switch, wherein the resistive-capacitive network includes: at least one impedance coupled between the first and second nodes; a first resistive element coupled between the second and third nodes; and a first capacitive element coupled between the second and fourth nodes; and a timer circuit coupled to the third node of the resistive-capacitive network and configured to generate a detection signal that is representative of the change in the voltage across the power semiconductor switch after switching on of the power semiconductor switch, wherein the timer circuit is configured to raise a level of the detection signal above a predetermined threshold voltage if the voltage across the power semiconductor switch does not fall below a predetermined value after switching on of the power semiconductor switch, and wherein the resistive-capacitive network is configured such that parasitic capacitances of the device are compensated or over compensated so as to prevent the timer circuit from raising the level of the detection signal above the predetermined threshold voltage if the voltage across the power semiconductor switch does fall below the predetermined value after switching on of the power semiconductor switch.
 2. The device as per claim 1, further comprising a clamping circuit configured to limit a voltage at the third node of the resistive-capacitive network to a maximum predetermined voltage.
 3. The device as per claim 2, wherein the maximum predetermined voltage corresponds to an ON-level of a gate-emitter driving signal of the power semiconductor switch.
 4. The device as per claim 1, wherein the fourth node is at a second reference potential.
 5. The device as per claim 1, wherein the at least one impedance compensates or overcompensates the parasitic capacities of the device.
 6. The device as per claim 1, wherein the at least one impedance comprises a capacitive element and a parallel resistive element.
 7. The device as per claim 1, wherein the resistive-capacitive network includes one or more further impedances in series with the at least one impedance between the first node and the second node of the resistive-capacitive network, each of which has a capacitive element and a parallel resistive element.
 8. The device as per claim 7, wherein the resistive-capacitive network includes a first further resistive element that is coupled parallel to the first capacitive element and a second further resistive element which is coupled in parallel to a second capacitive element of the resistive-capacitive network.
 9. The device as per claim 8, wherein the first and second further resistive elements are configured to limit a stationary voltage level across the first and second capacitive elements.
 10. The device as per claim 1, further comprising a second clamping circuit configured to limit a node between the resistive-capacitive network and the timer circuit to a minimum predetermined voltage.
 11. The device as per claim 10, wherein the minimum predetermined voltage corresponds to an OFF-level of a gate-emitter driving signal of the power semiconductor switch.
 12. The device as per claim 1, wherein the timer circuit includes a capacitance which is charged or discharged in response to a voltage level at the third node of the resistive-capacitive network and a resistive element, wherein a voltage level at one end of the capacitance is the detection signal.
 13. The device as per claim 1, wherein the timer circuit includes a digital circuit which is configured to sample a voltage level at the third node of the resistive-capacitive network and to generate the detection signal in response to the voltage level at the third node.
 14. The device as per claim 1, wherein the timer circuit has no active component.
 15. The device as per claim 1, wherein the resistive-capacitive network has a further capacitive element that is coupled between the second node and the first capacitive element, wherein the at least one impedance includes a capacitive element and a resistive element coupled in parallel to the capacitive element and wherein the resistive element is coupled to the second node and the capacitive element of the at least one impedance is coupled to the first capacitive element.
 16. The device as per claim 15, wherein the capacitive element of the first impedance is at least five times greater than the further capacitive element.
 17. The device as per claim 15, wherein the further capacitive element is arranged such that an influence of the first capacitive element on a voltage level at the second node is reduced.
 18. The device as per claim 15, wherein the further capacitive element is designed to reduce an amount of electrical charge that oscillates between the first capacitive element and the second node.
 19. The device as per claim 1, further comprising a further resistive element that is coupled between the third node and a reference potential and that is configured to partially set a stationary level of the detection signal.
 20. The device as per claim 1, wherein the timer circuit further includes a further resistive element, a diode, and a second capacitance which are configured to influence a dynamic level of the detection signal.
 21. A device for the detection of a short circuit or excess current situation in a power semiconductor switch, wherein the device comprises: a resistive-capacitive network having a first, a second, a third and a fourth node, wherein the resistive-capacitive network is to be coupled to a first terminal of the power semiconductor switch at the first node and to provide at the second node a signal that is representative of a voltage across the power semiconductor switch, wherein the resistive-capacitive network includes: at least one impedance coupled between the first and second nodes; a first resistive element coupled between the second and third nodes; and a first capacitive element coupled between the second and fourth nodes; a timer circuit coupled to the third node of the resistive-capacitive network and configured to generate a detection signal that is representative of the change in the voltage across the power semiconductor switch after switching on of the power semiconductor switch, wherein the timer circuit is configured to raise a level of the detection signal above a predetermined threshold voltage if the voltage across the power semiconductor switch does not fall below a predetermined value after switching on of the power semiconductor switch, and wherein the resistive-capacitive network is configured such that parasitic capacitances of the device are compensated or over compensated so as to prevent the timer circuit from raising the level of the detection signal above the predetermined threshold voltage if the voltage across the power semiconductor switch does fall below the predetermined value after switching on of the power semiconductor switch; and a comparator coupled to receive the detection signal and to transmit an error signal which indicates if the detection signal exceeds a reference signal.
 22. The device as per claim 21, wherein the reference signal is stationary.
 23. The device as per claim 21, wherein the timer circuit includes a capacitance which is charged or discharged in response to a voltage level at the third node of the resistive-capacitive network and a resistive element, wherein a voltage level at one end of the capacitance is the detection signal, the device further comprising a switch configured to clamp one end of the capacitance of the timer circuit to a fixed potential if the power semiconductor switch is switched off.
 24. The device as per claim 23, wherein the capacitor of the timing circuit is at least partially discharged if the one end of the capacitance of the timer circuit is clamped to a fixed potential if the power semiconductor switch is switched off.
 25. A control circuit for a power semiconductor switch, wherein the control circuit comprises: a device for the detection of a change in the voltage across a power semiconductor switch, wherein the device includes: a resistive-capacitive network having a first, a second, a third and a fourth node, wherein the resistive-capacitive network is to be coupled to a first terminal of the power semiconductor switch at the first node and to provide at the second node a signal that is representative of a voltage across the power semiconductor switch, wherein the resistive-capacitive network includes: at least one impedance coupled between the first and second nodes; a first resistive element coupled between the second and third nodes; and a first capacitive element coupled between the second and fourth nodes; a timer circuit coupled to the third node of the resistive-capacitive network and configured to generate a detection signal that is representative of the change in the voltage across the power semiconductor switch after switching on of the power semiconductor switch, wherein the timer circuit is configured to raise a level of the detection signal above a predetermined threshold voltage if the voltage across the power semiconductor switch does not fall below a predetermined value after switching on of the power semiconductor switch, and wherein the resistive-capacitive network is configured such that parasitic capacitances of the device are compensated or over compensated so as to prevent the timer circuit from raising a level of the detection signal above the predetermined threshold voltage if the voltage across the power semiconductor switch does fall below the predetermined value after switching on of the power semiconductor switch; a comparator coupled to receive the detection signal and to transmit an error signal which indicates if the detection signal exceeds a reference signal; and a drive circuit coupled to receive the error signal and to switch off the power semiconductor switch in response to the error signal indicating that the detection signal exceeds the reference signal.
 26. The control circuit as per claim 25, further comprising a power semiconductor switch coupled to be controlled by the drive circuit.
 27. The control circuit as per claim 25, wherein the voltage across the power semiconductor switch corresponds to a collector-emitter, an anode-cathode voltage, or a drain-source peak voltage of the power semiconductor switch.
 28. The control circuit as per claim 25, wherein a maximal nominal voltage in a switched-off state of the power semiconductor switch is more than 500 V.
 29. The control circuit as per claim 25, wherein a maximal nominal voltage in a switched-off state of the power semiconductor switch is more than 2 kV. 